Fully Reshapeable and Recyclable Protein Hydrogels.

Hydrogels have emerged as a new generation of functional materials with a broad range of applications in diverse fields. They usually cannot be reshaped or recycled, restricting their ability to respond to evolving demands and emerging applications, and contributing to the accumulation of synthetic polymer waste and associated environmental concerns. Here, a robust and general strategy is reported to engineer fully reshapeable and recyclable protein hydrogels by integrating protein folding-unfolding with reversible disulfide crosslinking. Taking advantage of the substantial stiffness contrast between protein hydrogels in their folded and unfolded protein states, protein hydrogels are reversibly reshaped across one-, two-, and three-dimensional geometries. Due to the denaturant concentration dependency and reversibility of the protein folding-unfolding process, the resulting reshaping is highly tunable, reproducible, and chemically erasable, enabling consecutive shape transformations from a single hydrogel precursor. To impart full recyclability, irreversible crosslinking chemistry is replaced with a dynamic disulfide-based one. The resulting hydrogels can be fully recycled, and the recovered proteins can be reused to form new hydrogels, allowing for complete recycling and repeated remolding of hydrogels into new shapes without compromising their mechanical properties. This approach establishes a robust platform for developing next-generation protein-based materials with dynamic formability and true material circularity.